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LIBRARY 


UNIVERSITY  OF  CALIFORNIA, 


RECEIVED    BY  EXCHANGE 


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Ube  mnix>ersft2  of 

FOUNDED  BY  JOHN  D.  ROCKEFELLER 


STUDIES  IN  RADIO-ACTIVITY 


A  DISSERTATION 

SUBMITTED    TO    THE    FACULTY    OF    THE    OGDEN    GRADUATE    SCHOOL    OF 

SCIENCE  IN  CANDIDACY  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 

(DEPARTMENT  OF  CHEMISTRY) 


t>7    f,i£ 


I  UNIVERSITY  I 


BY 

STEWART  JOSEPH  LLOYD 


1910 


TTbe  mniv>ersit£  of  Gbicaao 

FOUNDED   BY  JOHN   D     ROCKEFELLER 


STUDIES  IN  RADIO-ACTIVITY 


A  DISSERTATION 

SUBMITTED    TO    THE     FACULTY     OF    THE    OGDEN    GRADUATE    SCHOOL    OF 

SCIENCE  IN  CANDIDACY  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 

(DEPARTMENT  OF  CHEMISTRY) 


BY 

STEWART  JOSEPH  LLOYD 


UNIVERSITY 

OF 


1910 


Cte,1 


OF  THE 

(  UNIVERSITY  ) 

.IFOR  Nil 


THE  BETA  ACTIVITY  OF  URANINITE 


BY   STEWART  J.    I^OYD 

The  percentage  of  the  total  a  activity  of  uraninite  con- 
tributed by  each  radioactive  constituent  of  that  mineral  has 
been  made  the  subject  of  investigation  by  Boltwood, *  by 
McCoy  and  Ross,2  and  to  a  lesser  extent  by  Mme.  Curie.3 
Also  the  absolute  maximum  ionization  current  due  to  the 
activity  of  i  gram  uranium  in  the  forni  of  an  infinitely  thin 
film  has  been  determined  by  McCoy  and  Ashman4  in  con- 
nection with  their  work  on  uranium  oxide  as  a  standard  of 
radioactivity.  The  present  investigation  was  undertaken, 
at  the  suggestion  of  Prof.  McCoy,  with  a  view  to  ascertaining 
the  percentage  of  the  total  ft  activity  to  be  assigned  to  each 
constituent  of  Uraninite,  and,  if  possible,  to  determine  by 
comparison  with  the  a  activity  of  uranium  oxide  the  total 
ionization  currenf  produced  by  the  /?  activity  of  each. 

The  latter  object  was  however  found  impossible  of  realiza- 
tion. It  was  at  first  thought  that  possibly  the  3  rays,  like 
the  w,  might  possess  a  definite  fixed  range  beyond  which  they 
ceased  to  produce  ionization,  and  that  the  apparent  absorp- 
tion following  the  exponential  law  might  be  due  to  scattering 
alone;5  that  if  the  latter  effect  were  eliminated,  this  range 
might  be  determined  for  each  substance,  and  by  the  use  of  an 
electroscope  of  suitable  form  and  sufficient  size  the  total 
ionization  current  obtained,  just  as  in  the  case  of  the  a 
activity.  With  this  in  mind,  a  large  cylindrical  electroscope 
was  constructed,  in  which  the  active  material  emitting  the 
particles  could  be  placed  at  the  centre,  by  which  arrangement 
the  particles  "bent  out"  of  an  ordinary  p  ray  electroscope 
by  the  scattering  due  to  absorbing  material  would  be  re- 


1  Am.  Jour.  Sci.,  25,  269  (1908). 

2  Jour.  Am.  Chem.  Soc.,  29,  1697  (1907). 

3  Comptes  rendus,  126,  1101. 

4  Am.  Jour.  Sci.,  26,  521  (1908). 

5  Crowther:  Proc.  Roy.  Soc.,  8oA,  186  (1908). 


211029 


5io  Stewart  J.  Lloyd 

tained  within  the  ionization  chamber,  and  their  ionizing 
effect  included.  Upon  trial,  however,  it  was  discovered,  as 
has  recently  been  shown  also  by  Makower,1  that  actual  true 
absorption  as  well  as  scattering  of  the  /?  rays  does  take  place, 
so  that  a  determination  of  the  absolute  ionization  current  in 
a  way  comparable  to  that  used  for  the  «  rays  seemed  im- 
practicable. The  measurements  of  p  activity  in  this  paper 
are  therefore  merely  relative,  and  hold  accurately  only  for 
the  particular  electroscope  used.  The  order  of  magnitude 
will  be  the  same,  however,  whatever  measuring  vessel  may 
be  employed,  and  the  variations  from  the  numbers  here  given 
will  not  be  great,  so  that  the  latter  may  fairly  be  taken  as 
representing  the  relative  magnitudes  of  the  /?  activities  of  the 
different  substances. 

The  constituents  of  uraninite  known  to  emit  /?  rays 
capable  of  producing  appreciable  ionization  after  passing 
through  a  sheet  of  aluminium  foil  0.044  mm  thick  are  U  X, 
Ra  B,  Ra  C,  and  Ra  E2.  In  order  to  determine  their  respective 
activities  with  any  degree  of  accuracy  it  was  necessary  to 
devise  means  of  separating  them  quantitatively  not  only 
from  the  mineral  itself,  but  from  any  considerable  amount  of 
foreign  substances  introduced  during  their  extraction.  Prac- 
tically no  work  has  been  done  on  the  separation  of  the  radio- 
active substances  in  a  quantitative  way,  and  very  little  on 
their  general  chemical  properties,  consequently  the  latter 
were  studied  in  some  detail,  especially  in  the  case  of  U  X. 
In  the  following  pages  therefore,  after  a  description  of  the 
electroscope  used,  there  will  be  found  measurements  of  the  ft 
activity  of  uraninite,  U  X,  Ra  B,  Ra  C  and  Ra  E2,  referred  to 
the  amounts  associated  with  i  gram  of  uranium  as  a  unit; 
descriptions  of  the  methods  found  convenient  for  obtaining 
these  substances  in  a  condition  suitable  for  measurement, 
and  the  results  of  a  few  other  measurements  of  related  in- 
terest. 

The  electroscope  used  in  practically  all  the  measure- 
ments is  that  shown  in  Fig.  i.  It  was  designed  especially 

1  Phil.  Mag.,  [6]  17,  171  (1909). 


The  Beta  Activity  of  Uraninite  511 

for  the  examination  of  /?  activity,  and  differs  from  electro- 
scopes commonly  used  for  that  purpose  in  allowing  the  active 
material  to  be  placed  either  at  the  centre  or  at  the  bottom 
of  the  ionization  chamber,  instead  of  outside.  It  was  made  of 
galvanized  iron,  had  a  diameter  of  40  cm1  and  the  same  height. 
As  it  was  feared  that  the  highest 
potential  difference  that  could  con- 
veniently be  used,  about  500  volts, 
would  be  insufficient,  with  such  an 
instrument,  to  give  a  potential 
gradient  high  enough  to  produce 
the  saturation  current,  four  upright 
brass  rods  were  attached  to  the 
base,  each  at  a  distance  of  7  cm 
from  the  centre,  and  four  similar 
rods,  attached  to  the  central  elec- 
trode as  shown  in  the  figure,  were 
placed  between  and  outside  them. 
In  this  way  there  was  obtained  a 
potential  gradient  of  not  less  than 
75  volts  per  cm  throughout  the 
ionization  chamber,  except  at  a  very  c-  Charsing  wire- 

D.  Branches  of  central  electrode. 

few  points.     Separate  experiments 

showed  that  with  this  arrangement  the  saturation  current 
was  being  obtained  with  /?  ray  preparations  of  ordinary 
strength.  The  central  electrode  and  the  rods  attached  to  it 
could  be  rotated  at  will.  A  door  sliding  vertically  afforded 
access  to  the  interior  of  the  electroscope.  The  central  elec- 
trode was  made  up  of  two  sections  screwing  into  each  other, 
so  that  preparations  could  be  measured,  if  desirable,  at  the 
centre.  In  most  of  the  measurements,  however,  the  active 
material  was  placed  on  the  bottom  of  the  ionization  chamber. 
As  a  standard  of  activity,  a  film  of  uranium  oxide  pre- 
pared accord  ng  to  the  method  of  McCoy  and  Ashman2  was 
employed.  It  may  be  of  interest  to  note  that  the  /?  activity 


Fig.  i 

E.  Rods  attached  to  base. 

A.  Ionization  chamber. 

F.  Gold  leaf  electroscope. 

B.  Central  electrode. 


1  The  electroscope  was  cylindrical  instead  of  square  as  shown  in  Fig.  i. 

2  Am  Jour.  Sci.,  26,  521  (1908). 


512  Stewart  J.  Lloyd 

of  such  a  film  (weighing  0.753  gram)  measured  in  an  ordinary 
a  ray  electroscope  such  as  that  used  in  this  laboratory  by 
McCoy  and  Ashman  constitutes  hardly  4  percent  of  the 
whole;  in  the  electroscope  just  described  it  amounts  to  12 
percent.  The  ratio  of  the  volumes  of  the  two  electroscopes 
is  1-9.5. 

Uraninite 

In  measuring  the  /?  activity  of  uraninite  it  is  necessary 
of  course  to  take  account  of  the  absorption  due  to  the  mineral 
itself,  just  as  in  the  measurements  of  the  a  activity,  though 
the  effect  is  of  less  magnitude  here.  Hence  three  films  of 
each  of  two  samples  of  uraninite  free  from  thorium,  one  con- 
taining 58.1  percent  U,  the  other  45.1  percent  were  measured; 
the  ratio  of  weight  to  activity  plotted  against  the  weight,  and 
this  ratio  for  an  infinitely  thin  film,  where  no  absorption  takes 
place,  determined  graphically.1  The  activities  are  given  in 
terms  of  the  standard  referred  to  above,  divided  by  100  to 
avoid  decimals.  As  was  first  pointed  out  by  Boltwood,2  a 
small  part  of  the  emanation  is  spontaneously  evolved  when 
uraninite  is  powdered,  and  hence  Ra  B  and  Ra  C  are  present 
in  thin  films  in  less  than  equilibrium  amount.  It  will  be 
shown  later  that  Ra  B  and  Ra  C  together  contribute  52  percent 
of  the  total  /?  activity  of  uraninite.  The  amount  of  emana- 
tion and  hence  the  /?  activity  lost  was  determined  essential!)7 
as  described  by  McCoy  and  Ross,3  namely  by  boiling  off  in 
a  mixture  of  nitric  and  sulphuric  acids  the  emanation  from  a 
weighed  quantity  of  the  powdered  mineral,  sealing  up  the 
mixture  to  allow  the  emanation  to  accumulate  again,  boiling 
off  and  measuring  once  more,  and  calculating  the  maximum 
amount  of  emanation,  using  as  period  3.75  days.  Since  the 
/?  activity  of  the  immediate  emanation  products  Ra  B  and 
Ra  C  constitutes  52  percent  of  the  whole,  evidently  the  activity 
found  requires  to  be  increased  by  the  activity  of  52  percent  of 


1  McCoy:   Jour.  Am.  Chem.  Soc.,  27,  402  (1905). 

2  Phil.  Mag.,  [6]  9,  603  (1905). 

3  Jour.  Am.  Chem.  Soc.,  29,  1698  (1907). 


The  Beta  Activity  of  Uraninite 


the  emanation  lost  in  this  way.     This  correction  is  applied 
in  the  following  table. 

The  a  activity  was  excluded  by  covering  the  films  with 
sheet  of  aluminium  foil.  The  amount  of  /?  activity  cut  off 
by  the  foil  was  determined  graphically  by  adding  successively 
i,  2,  3,  and  4  layers  of  foil,  and  producing  the  curve,  activity- 
foils,  backwards.  It  was  found  that  one  sheet  of  aluminium 
foil  0.044  mm  thick  cut  off  13.65  of  the  total  /?  activity  of 

uraninite. 

Uraninite,  58.1   Percent  U 


Weight 

Activity 

Em.  lost 

Corr. 
act. 

w\a 

1     • 
a0  per 
wja0      g.  uran- 
inite 

a0  per 

g.  u. 

0.2175 
0.4100 
0-6934 

6.841 
II  .42 
12.59 

4.2  %  of 
total 
emanation 

7.01 
11.68 
12.87 

0.0312 
0.0352 
0-0539 

0.0307     32.6 

56.1 

Uraninite,  45.1   Percent  U 


Weight 

Activity 

Em.  lost 

Corr. 
act. 

w\a 

w\aQ 

g"-!ner 

inite  g'  l 

0.3398 
0.4422 
0.6650 

7.713 
9-365 
10.23 

3-8  %  of 
total 
emanation 

7.87 

9-55 
10.44 

0.0431 
o  .  0463 
0.0637 

0.04 

25-0  55-4 

In  the  preceding  tables  w  refers  to  the  weight  of  the  film 
of  mineral,  a  to  the  activity  thereof,  and  a0  to  the  activity 
of  an  infinitely  thin  film,  determined  graphically  as  described 
above. 

The  average  of  the  two  values  for  a0  per  gram  U  is  55.75. 
That  is,  the  £1  activity  of  an  infinitely  thin  film  of  uraninite 
containing  i  gram  uranium  and  all  the  successive  products 
of  the  latter  in  equilibrium  amounts,  is,  in  the  electroscope 
described,  0.5575  times  as  great  as  the  total  activity  of  the 
standard  film  of  uranium  oxide  employed. 

Uranium  X 

As  it  has  repeatedly  been  shown  that  uranium  X  is 
produced  by  uranium,  and  since  uranium  itself  is  readily 


514  Stewart  J.  Lloyd 

determined  quantitatively  in  uraninite,  it  seemed  much 
simpler,  instead  of  separating  U  X  from  uraninite,  to  separate 
it  quantitatively  from  some  pure  compound  of  uranium 
which  contained  it  in  equilibrium  amount.  This  separation 
may  be  effected  to  a  greater  or  less  extent  in  several  ways; 
a  quantitative  separation,  however,  in  which  all  of  the  U  X 
is  obtained  without  any  uranium,  and  in  addition  sensibly 
free  from  other  impurities,  is  distinctly  difficult. 

The  compound  of  uranium  most  readily  obtained  is  the 
nitrate.  Uranium  X  has  been  obtained  from  it  in  several 
different  ways : 

1.  By  dissolving  uranium  nitrate  in  ether,  and  separa- 
ting the  aqueous  layer,  which  contains  most  of  the  U  X  and  a 
little  U.     This  separation  is  not  quantitative.1 

2.  By    precipitating    uranium    nitrate    with    ammonium 
carbonate  and  dissolving  in  excess,  whereby  the  U  X  remains 
undissolved.     This    also    is    incomplete,     and    requires    the 
presence  of  a  considerable  amount  of  impurity,  such  as  iron, 
to  make  it  of  any  use  whatever.1 

3.  By    precipitating    barium    sulphate    in    the    aqueous 
uranium    nitrate    solution,    whereby  U   X   is    carried    down 
mechanically.     Three  successive  operations  of  this  kind  re- 
move all  the  U  X.     It  was  found  possible  also  to  remove  the 
U  X  from  the  sulphate  precipitate  by  boiling  with  hot  concen- 
trated hydrochloric  acid,  but  to  obtain  a  complete  extraction 
acid  of  such  concentration  had  to  be  used  that  appreciable 
quantities  of  barium  sulphate  were  also  dissolved.2 

4.  By  stirring  into  an  acetone  solution  of  uranium  nitrate 
some   freshly   prepared   ferric    hydroxide.     Results   obtained 
by  this  method  proved  very  erratic,  from  40-90  percent  of  the 
U  X  being  removed,  never  more,  even  after  several  operations.3 

5.  By    boiling    aqueous    uranium    nitrate    with    animal 
charcoal.4     This     method     also     was     not     quantitative.     A 

1  Crookes:  Proc.  Roy.  Soc.,  66,  409  (1900). 

2  Becquerel:  Comptes  rendus,  133,  977  (1901). 

3  Moore  and  Schlundt:  Phil.  Mag.,  [6]  12,  393  (1906). 

4  Levin:  Phys.  Zeit.,  8,  585. 


The  Beta  Activity  0}  Uraninite  515 

modification  of  it,  in  which  soot  was  substituted  for  animal 
charcoal,  and  acetone  for  water  proved  to  be  quantitative, 
however,  and  entirely  satisfactory.  It  was  found,  also, 
more  convenient  to  stir  the  soot  into  the  acetone  than  to  boil 
it  with  the  latter. 

The  complete  process  employed  in  the  separation  was  as 
follows:  Five  or  10  grams  of  uranium  nitrate,  containing 
about  50  percent  U  were  dissolved  in  150  cc  of  acetone,  and 
stirred  for  thirty  mimites  with  i  gram  of  soot  prepared  by 
burning  naphthalene.  The  soot  need  not  be  purified  before 
using,  as  the  colored  hydrocarbons  and  other  substances  in  it 
are  removed  later,  and  the  fresher  the  soot  the  more  efficient 
it  appeared  to  be.  The  mixture  of  soot  and  acetone  was  then 
filtered,  another  gram  of  soot  added  to  the  uranium  nitrate- 
acetone  filtrate,  and  the  stirring  repeated.  Three  treatments 
of  this  kind  suffice.  Separate  experiments  showed  that  95 
percent  of  the  U  X  was  removed  in  the  first  treatment,  and 
practically  all  in  the  first  and  second  together.  Upon  rapid 
evaporation  of  the  filtrate  and  measurement  of  the  uranium 
oxide  produced  by  ignition,  scarcely  a  trace  of  /?  activity 
could  be  detected.  The  three  portions  of  soot  were  then 
united,  and  without  washing  boiled  twice  with  dilute  hydro- 
chloric acid  for  fifteen  minutes  at  a  time,  the  first  boiling  re- 
moving about  95  percent  of  the  U  X.  This  dissolves  out  from 
the  soot  the  U  X  and  the  small  amount  of  uranium  nitrate 
which  had  adhered  to  the  soot.  The  latter  can  not  be  re- 
moved even  by  prolonged  washing  of  the  soot  with  ether, 
alcohol  or  water.  This  solution  was  then  evaporated  to  a 
volume  of  100  cc,  0.05  gram  iron  wire  added,  and  when  the 
latter  had  dissolved,  ammonium  carbonate  was  added  care- 
fully until  the  uranium  had  just  redissolved.  Separate  ex- 
periments showed  that  this  amount  of  iron  was  sufficient  to 
carry  down  all  the  U  X,  and  that  no  uranium  remained  in  the 
precipitate.  Without  the  iron  the  separation  is  quite  in- 
complete. The  ferric  hydroxide-U  X  precipitate  was  then 
thoroughly  washed  with  water,  and  dissolved  in  10  cc  of 
hydrochloric  acid.  The  resulting  solution  was  shaken  three 


516  Stewart  J.  Lloyd 

times  with  ether  which  had  been  saturated  with  gaseous 
hydrochloric  acid,  whereby  the  ferric  chloride  dissolved  in 
the  ethereal  layer,  and  the  U  X  with  an  inappreciable  amount 
of  the  iron  salt,  remained  in  the  aqueous,  acid  layer.  If 
concentrated  acid  is  used,  and  the  ether  is  freshly  distilled, 
this  separation  is  quite  sharp.  The  uranium  X  solution  was 
then  evaporated,  finally  on  a  gold  plate,  and  its  activity 
measured. 

Two  samples,  each  containing  10  grams  uranium  nitrate, 
which  upon  analysis  yielded  47.36  percent  U,  were  treated 
as  indicated  above,  and  the  resulting  activity  measured  in 
the  electroscope.  The  residue  on  the  plate  weighed  in  one 
case  0.0015  gram  in  the  other  0.0027  gram,  and  had  therefore 
no  appreciable  absorbing  power  for  /?  rays.  As  is  well  known, 
U  X  emits,  besides  its  j  rays,  radiation  of  two  kinds,  "hard" 
penetrating  rays,  and  "soft"  rays  which  are  unable  to  pass 
through  0.044  mm  °f  aluminium  foil.  Since  in  the  measure- 
ment of  uranium  itself  these  rays  were  excluded  by  the  cover- 
ing of  foil,  it  became  necessary  to  determine  here  what  per- 
centage of  the  total  activity  of  the  U  X,  as  measured  in  this 
electroscope,  was  due  to  them.  The  preparation  was  there- 
fore covered  successively  by  i,  2,  and  3  layers  of  aluminium 
foil,  and  by  extrapolation  the  required  value  found.  It  was 
found  that  26.7  percent  of  the  total  ionization  due  to  U  X  was 
contributed  by  these  soft  rays. 

Schmidt1  and  others  have  recently  shown  that  these  soft 
rays  are  not  a  rays  of  short  range,  as  had  once  been  supposed, 
but  ft  rays  of  slight  penetrating  power.  The  above  measure- 
ment affords  additional  evidence  of  a  distinctly  different 
kind  in  favor  of  this  view,  as  is  shown  by  the  following  con- 
siderations. 

The  ratio  of  the  activities  due  to  the  two  kinds  of  rays 
in  an  ordinary  a  ray  electroscope  is  approximately  as  7-3. 
Had  the  weaker  radiation  been  a  in  character  and  of  short 
range,  its  effect  would  not  have  increased  in  magnitude  when 
measured  in  the  larger  electroscope,  while  the  activity  due  to 

1  Jahrb.  fur.  Rad.,  5,  451  (1908). 


The  Beta  Activity  of  Uraninite 


517 


the  penetrating  /?  rays  increases  about  threefold  (page  512). 
Hence  in  the  present  electroscope  the  ratio  of  the  two  activities 
would  have  been,  had  the  weaker  been  a  in  character,  about 
7-1  instead  of  3-1  as  it  is. 

The  following  table  gives  the  data  obtained  for  two 
samples  of  uranium  nitrate.  Allowance  was  made  of  course 
for  the  time  elapsing  between  the  separation  of  the  U  X  from 
the  uranium  nitrate  and  the  measurements. 


Weight  of 
uran.  nitrate 
grams 

Weight  of 
uran. 

Activity 

| 

Activity  of 
hard  rays 

Activity  of 
hard  rays 
per  g.  U. 

10 
IO 

tnl 

114.6 
116.9 

83-83 
85.72 

17.7 
18.1 

Mean  of  two  values 

17.9. 

Percentage  of  total  ft  activity  of  uraninite  due  to  hard 
rays  of  U  X,  No.  32.1. 

The  activity  of  one  of  these  preparations  was  measured 
over  several  months  with  the  object  of  redetermining  the 
period  of  U  X.  Both  hard  and  soft  radiations  decayed  at  the 
same  rate,  indicating  a  period  of  22.4  days. 

The  activity  of  U  X  was  determined  in  still  another  way. 
Three  films  of  uranium  oxide  were  prepared,  allowed  to 
stand  until  they  had  grown,  their  maximum  amounts  of  U  X, 
and  then  measured,  the  absorption  due  to  the  oxide  itself, 
and  the  a  radiation,  being  allowed  for  as  in  the  case  of 
uraninite.  The  results  were  found  to-  agree  essentially  with 
those  obtained  from  the  measurements  on  pure  U  X  extracted 
from  pure  uranium  nitrate. 


Weight  of 
U308 

Activity 

w\a 

w/a0 

Activity  per 

g.u. 

0.625 
0.694 
0.782 

8.941 
9-734 
9-731 

0.0692 
0.0713 
0.0761 

0.0675 

17-45 

518  Stewart  J.  Lloyd 

It  was  observed  also  that  one  layer  of  aluminium  foil 
0.044  mm  thick  cut  off  8.7  percent  of  the  /3  activity  of  U  X 
(hard  rays). 

Radio-Uranium 

In  a  recent  article  Danne1  has  published  some  measure- 
ments which  may  indicate  the  existence  between  uranium  and 
U  X  of  a  ray  less  substance  which  produces  U  X,  and  to  which 
he  has  given  the  name  radio-uranium.  This  substance  was 
obtained  by  him  along  with  U  X  by  precipitating  barium 
sulphate  in  an  aqueous  solution  of  uranium  nitrate.  As 
some  irregularities  and  peculiarities  had  been  observed  in 
the  course  of  the  present  work  on  U  X,  it  was  thought  worth 
while  to  attempt  the  detection  of  this  new  substance,  in  an 
indirect  way  at  least. 

If  such  a  substance  exists,  and  has  a  period  at  all  com- 
parable in  length  with  that  of  U  X,  and  if  the  uranium  nitrate 
be  freed  at  once  from  it  and  from  U  X,  the  rate  of  growth  of  the 
uranium  nitrate  in  /?  activity  should  be  much  different  from 
what  it  would  be  if  the  uranium  directly  produced  U  X.  Even 
if  the  uranium  nitrate  be  only  partially  freed  from  this  hy- 
pothetical substance,  the  recovery  curve  of  /?  activity  should 
still  be  somewhat  different  from  what  has  been  regarded  as 
the  normal,  the  difference  depending  upon  the  amount  of 
radio-uranium  removed.  Danne  obtained  his  radio-uranium 
by  precipitation  of  aqueous  uranium  nitrate  with  barium 
sulphate,  and  subsequent  elaborate  treatment  of  the  precipitate. 
In  the  present  experiment  therefore,  10  grams  of  uranium 
nitrate  were  dissolved  in  water,  and  barium  sulphate  pre- 
cipitated in  the  solution  twenty-five  times  successively. 
The  uranium  nitrate,  from  which,  presumably  at  least,  part 
of  the  radio-uranium  had  been  removed,  was  then  precipitated 
with  ammonia,  ignited  to  the  oxide  and  made  into  a  film. 
Measurements  of  the  growth  of  /?  activity  extending  over 
seventy  days  gave  a  period  of  22.7  days,  practically  the  same 
as  that  so  frequently  observed  for  U  X.  Hence,  if  such  a 

1  Le  Radium,  6,  42  (1909). 


The  Beta  Activity  of  Uraninite  519 

product  does  exist,  and  is  the  parent  of  U  X,  it  is  obviously 
not  removed  by  barium  sulphate.  Indeed  the  phenomena 
observed  by  Danne  could  all  be  accounted  for  by  the  assump- 
tion that  his  uranium  nitrate  had  not  been  freed  entirely 
from  radium. 

Chemical  Behavior  of  Uranium  X  • 

In  the  attempt  to  devise  a  suitable  method  for  extracting 
UX  from  uranium  nitrate  some  new  and  interesting  facts  with 
regard  to  the  chemical  behavior  of  the  latter  were  obtained. 
As  the  chemical  properties  of  the  less  abundant  radioactive 
substances  will  probably  assume  considerable  importance 
in  the  future,  especially  in  the  light  of  the  possible  position 
of  the  latter  in  the  periodic  table,  these  facts  are  given  below. 

Uranium  X,  as  has  been  observed  by  other  investigators, 
resembles  ferric  iron  very  closely  in  all  its  reactions.  It  is 
precipitated  quantitatively  from  its  hot  hydrochloric  acid 
solution  by  the  addition  of  a  small  amount  of  ferric  chloride 
and  ammonia.  This  reaction  affords  a  means  of  determining 
the  amount  of  U  X  in  a  solution  which  is  much  more  accurate 
and  rapid  than  the  evaporation  of  the  solution  and  subse- 
quent measurement.  The  amount  of  iron  added  need  not  be 
so  great  as  to  cause  any  appreciable  absorption  of  the  activity. 

When  to  a  hydrochloric  acid  solution  of  U  X,  ferric 
chloride  and  aluminium  chloride  are  added,  the  two  metals 
precipitated  by  potassium  hydroxide  and  excess  of  the  latter 
added,  the  uranium  X  remains  undissolved,  with  the  iron,  not 
a  trace  following  the  aluminium. 

Ammonium  carbonate,  when  added  to  a  precipitate  of 
ferric  hydroxide  containing  U  X,  dissolves  a  small  amount  of 
the  iron  when  cold,  and  quite  a  considerable  amount  when 
hot.  The  U  X  is  much  less  soluble  in  the  carbonate  than  is 
the  iron,  being  scarcely  dissolved  at  all. 

The  only  way  known  by  which  UX  can  be  completely 
separated  from  iron  is  by  treatment  with  ether  and  hydro- 
chloric acid  (page  516).  This  reaction  is  of  importance,  as  the 
most  convenient  method  of  obtaining  U  X  from  a  solution  is 
by  precipitation  with  ferric  hydroxide. 


520  Stewart  J  .  Lloyd 

Uranium  X  when  precipitated  from  a  solution  of  uranium 
nitrate  by  barium  sulphate  is  not  dissolved  out  by  boiling 
sodium  carbonate,  but  remains  with  the  resulting  barium 
carbonate. 

Lead  sulphate  is  not  so  efficient  in  carrying  down  U  X 
as  is  barium  sulphate,  the  ratio  being  7-10.  When  lead 
sulphate  containing  U  X  is  treated  with  sodium  thiosulphate, 
the  U  X  does  not  follow  the  lead,  provided  there  is  sufficient 
impurity  present  to  form  a  nucleus  of  undissolved  matter. 

Ammonium  acetate  removes  from  a  lead  sulphate  —  U  X 
precipitate  about  35  percent  of  the  U  X  in  two  extractions. 

The  precipitation  of  basic  ferric  acetate  in  a  solution  of 
U  X  carried  down  70  percent  of  the  activity. 

Boiling  acetic  acid  does  not  remove  'any  pf  the  activity 
from  a  barium  sulphate-U  X  precipitate. 

Radium  B  and  C 

Rutherford's1  examination  of  the  immediate  active  de- 
posit from  radium  led  him  to  the  conclusion  that  radium  C 
alone  emitted  /?  rays.  Certain  irregularities  in  the  decay 
curves  however  brought  about  subsequent  investigations  by 
Schmidt,2  and  by  Bronson,3  both  of  whom  demonstrated  the 
existence  of  /?  activity  in  radium  B,  the  latter  showing  that  the 
/?  activity  of  B  probably  exceeded  that  of  C.  The  results  of 
their  work,  so  far  as  the  existence  of  /?  activity  in  radium  B 
is  concerned  were  substantiated  by  Duane,4  using  a  very 
different  experimental  method.  He  measured  the  amount  of 
negative  electricity  emitted  by  the  active  deposit  instead  of 
the  ionization  current  due  to  it.  In  the  present  investigation 
the  total  p  activity  due  to  B  and  C  together  was  obtained, 
and  by  an  indirect  method  the  ratio  of  the  two  activities,  from 
which  data  the  individual  activities  themselves  were  calculated. 

To  determine  the  total  /?  activity  of  the  active  deposit  of 
radium,  that  is,  the  /?  activity  of  B  and  C  together,  portions 


1  Phil.  Trans.,  198  (1904). 

2  Phys.  Zeit.,  6,  897;  7,  764. 

3  Phil.  Mag.,  [6]  12,  73(1906). 

4  Le  Radium,  5,  65. 


The  Beta  Activity  of  Uraninite  521 

of  a  radium  solution  were  evaporated  on  platinum  plates, 
allowed  to  stand  for  forty  days,  at  the  end  of  which  time  the 
activity  had  reached  a  maximum,  and  then  measured  in  the 
electroscope,  interference  by  the  emanation  and  by  the  a 
activity  in  general  being  prevented  by  a  closely  adhering 
sheet  of  aluminium  foil.  The  amount  of  ft  activity  absorbed 
by  the  foil  was  determined  essentially  as  in  previous  similar 
cases.  The  radium  films  themselves  were  so  thin  that  no  ap- 
preciable absorption  took  place  in  them.  In  order  to  deter- 
mine the  amount  of  radium  of  which  the  activity  was  being 
measured,  portions  of  the  same  radium  solution  were  com- 
pared in  a  gas  electroscope  with  a  weighed  amount  of  uraninite 
whose  uranium  and  hence  radium  content  was  known. 
Boltwood,1  however,  had  previously  shown  that  radium 
preparations  in  the  form  of  thin  films  lose  spontaneously 
quite  considerable  amount  of  emanation,  and  that  therefore 
the  maximum  activity  of  a  radium  preparation  was 
less  than  it  should  be,  were  all  the  emanation  retained. 
Since  a  correction  for  the  loss  of  emanation  was  made  in 
the  case  of  uraninite,  and  since  in  any  event  the  losses  for 
the  two  materials  are  by  no  means  proportional,  it  was 
necessary  to  make  a  similar  correction  here.  To  do  this, 
a  portion  of  the  same  radium  solution  was  evaporated 
on  a  small  thin  copper  plate,  the  activity  allowed  to  reach  a 
maximum,  the  plate  placed  bodily  in  a  small  flask,  and  the 
emanation  boiled  off  and  measured  in  the  usual  way.  The 
flask  was  then  sealed  up,  the  emanation  allowed  to  grow  for 
a  few  days,  measured  again,  and  the  maximum  amount 
calculated.  Three  determinations  of  this  kind  gave  10.7, 
1 1. 6,  and  11.4  percent  of  emanation  lost,  an  average  of  11.2. 
The  correction  is  applied  in  the  accompanying  tables. 


| 

No. 

Act.                  Corr.  act. 

Act.  per  g.  U 

Average 

1 

i 

I 

10.  61 

12  .2 

28.7 

— 

2 

11.13 

12.8 

29.9 

29.0 

3                    10.  i                   11.4 

28.5 

Phil.  Mag.,  [6]  9,  603  (1905). 


522 


Stewart  J.  Lloyd 


Percentage  of  the  total  /?  activity  of  uraninite  contributed 
by  B  and  C  51.8. 

The  total  /?  activity  due  to  the  active  deposit  of  radium 
was  obtained  in  still  another  way,  after  the  method  used  by 
McCoy  and  Ross1  for  obtaining  the  a  activity  due  to  emana- 
tion +  A  +  B  +  C  in  uraninite.  A  portion  of  the  uraninite 
sample  containing  58.1  percent  uranium  was  finely  ground, 
treated  with  nitric  acid,  evaporated  to  dryness,  and  the 
process  repeated  three  times  at  intervals  of  two  hours,  to  free 
the  material  from  emanation  and  to  allow  A,  B  and  C  to 
decay.  After  the  last  evaporation  the  residue  was  heated 
strongly  enough  to  decompose  all  the  nitrates  present.  The 
resulting  residue,  mostly  oxides,  was  made  into  films  as 
quickly  as  possible,  and  its  activity  determined  in  the  usual 
way.  The  films  were  then  allowed  to  stand  until  the  maxi- 
mum ft  activity  had  been  attained,  about  35  days.  The 
percentage  of  the  total  /?  activity  contributed  by  the  active 
deposit  could  thus  be  directly  calculated.  The  results  are 
contained  in  the  following  table. 


Initial  ft  activity 
(due  to  constituents 
other  than  BandC) 

Final  £  activity 
(due  to  all  con 
stituents  ) 

Act.  corr.  for  loss 
of  eman. 

Act.  of  B  +  C 

4.24 
5.98 

8.27 
11.72 

8.8 

12  .46 

4-56 
6.48 

Percentage  of  /?  activity  of  uraninite  contributed  by 
B  and  C  therefore  52.0. 

The  /?  rays  from  uranium  X,  radium  B,  radium  C  and 
radium  E2  are  unequally  absorbed"  by  the  uranium  oxide, 
and  as  no  allowance  for  absorption  was  made  in  these  measure- 
ments, the  close  agreement  between  them  and  those  im- 
mediately preceding  is  fortuitous  only. 

To  determine  the  individual  /?  activities  of  Ra  B  and 
Ra  C  advantage  was  taken  of  the  difference  in  the  tempera- 
tures at  which  they  volatilize.  A  copper  plate  kept  negatively 


Jour.  Am.  Chem.  Soc.,  29,  1702  (1907). 


The  Beta  Activity  of  Uraninite  523 

charged  was  placed  in  a  vessel  containing  emanation,  and 
allowed  to  remain  until  the  deposit  on  it  had  reached  a  state 
of  radioactive  equilibrium.  It  was  then  removed,  allowed 
to  stand  for  twenty  minutes  to  ensure  the  complete  decay  of 
Ra  A,  and  the  ratio  of  its  a  to  its  p  activity  measured.  The 
P  activity  was  due  to  B  and  C  together,  the  a  activity  to  C 
alone.  Another  plate  which  had  been  exposed  in  a  similar 
way  was  heated  for  five  minutes  in  an  electric  furnace  to  a 
temperature  of  700°  C.  According  to  Makower,1  Ra  B 
volatilizes  entirely  at  this  temperature,  while  Ra  C  is  un- 
affected. The  ratio  of  the  a  to  the  p  activity  was  then 
measured,  both  activities  in  this  case  being  due  to  Ra  C. 
From  these  two  measurements  the  individual  activities  were 
calculated 

Let  x  ==  p  activity  of  Ra  C. 
y  ==  P  activity  of  Ra  B. 
z  =  a  activity  of  Ra  C  when  all  are  in  radioactive 

equilibrium. 

Then  z/x  +  y  ==  ratio  of  a  to  p  activity  after  exposure 

to  emanation  and  decay  of  RaA  =  mr 

z/x  «  ratio  of  a  to  p  activity  after  heating  to 

volatilize  Ra  B   =  w2, 
m,  —  mv 


The  results  of  several  measurements  did  not  agree  very 
closely  among  themselves,  as  might  be  expected  from  the 
fact  that  at  the  time  of  measurement,  B  and  C  are  not  present 
in  equilibrium  amount.  In  general,  however,  it  appeared 
that  of  the  total  p  activity  due  to  B  and  C,  radium  C  con- 
tributed about  68  percent,  Ra  B  about  32  percent. 

Percentage  of  total  activity  of  uraninite  due  to   B  is  15.9 

'   C    "    35-9 

Radium  E, 

The  determination  of  the  p  radiation  of  E2  was  some- 
what more  difficult  than  that  of  any  one  of  the  preceding 


Proc.  Manch.  Phil.  Soc.,  53,  II,  1-8. 


524  Stewart  ] .  Lloyd 

substances.  Radium  B  and  C  depend  immediately  upon  the 
easily  estimated  radium  emanation,  while  uranium  X  may  be 
grown  readily  from  weighable  quantities  of  uranium. 
Radium  E2  may,  indeed,  be  obtained  without  trouble  from 
Ra  D,  but  the  quantitative  extraction  of  Ra  D  from  uraninite 
had  not  been  worked  out.  Possibly  the  most  satisfactory 
though  rather  tedious  way  to  obtain  the  desired  result  would 
be  to  obtain  a  strong  preparation  of  Ra  D,  await  the  growth 
in  it  of  Et,  E2  and  F,  and  when  equilibrium  had  been  reached, 
measure  the  activity  of  Ra  F,  the  only  a  ray  product  present. 
Since  the  activity  of  F  in  terms  of  uraninite  has  been  deter- 
mined,1 we  should  know  the  weight  of  mineral  corresponding 
to  the  amount  of  Ra  D  in  our  sample  and  could  then  deter- 
mine E2  with  accuracy.  No  supply  of  Ra  D  with  its  products 
was  available,  however,  so  that  it  became  necessary  to  study 
the  quantitative  extraction  of  the  latter  from  uraninite,  and 
to  obtain  Ra  E2  from  it  in  such  a  manner  as  to  allow  of  its 
activity  being  measured.  A  preparation  of  Ra  D  was  made 
however,  set  aside  to  permit  of  the  growth  of  Ra  F,  and  will 
be  measured  later. 

In  order  to  determine  the  conditions  under  which  Ra  D 
could  be  extracted  quantitatively  from  uraninite,  a  study  of 
its  chemical  behavior  was  made.  As  its  name  radio-lead 
would  indicate,  it  clings  very  closely  to  lead,  quite  as  closely 
as  U  X  does  to  ferric  iron,  following  the  lead  quantitatively 
everywhere,  provided  a  sufficient  amount  of  the  latter  is 
present.  In  the  form  of  sulphate  it  dissolves  quantitatively 
in  ammonium  acetate  and  in  sodium  thiosulphate,  is  pre- 
cipitated quantitatively  by  hydrogen  sulphide,  sulphuric 
acid,  and  by  sodium  carbonate.  If  the  quantity  of  lead 
associated  with  it  be  small,  however,  some  of  the  Ra  D  is 
lost.  The  one  condition  to  be  fulfilled  in  order  that  Ra  D 
may  follow  quantitatively  the  reactions  of  lead  appears  to  be 
the  presence  of  considerable  quantities  of  that  metal. 

In  obtaining  Ra  D  from  uraninite  therefore,  the  follow- 
ing method  was  used. 

1  Boltwood:  Am.  Jour.  Sci.,  25,  269  (1908). 


The  Beta  Activity  of  Uraninite  525 

10  grams  uraninite  containing  58.1  per  cent  U  were  dis- 
solved in  dilute  nitric  acid.  The  uraninite  was  practically  free 
from  sulphides,  so  that  oxidation  of  the  latter  to  sulphates  was 
not  feared.  The  residue,  mostly  silica,  showed  activity,  which 
disappeared  in  a  few  hours.  The  solution  was  evaporated 
to  dryness,  100  mg  of  lead  nitrate  added,  and  solution  effected 
by  the  addition  of  water  and  a  few  drops  of  nitric  acid.  Dilute 
sulphuric  acid  was  then  added  to  precipitate  the  sulphates 
of  barium  and  lead.  The  mixed  sulphates  were  then  ex- 
tracted repeatedly  with  ammonium  acetate,  to  remove  the 
lead  and  radio-lead,  and  the  resulting  solution  precipitated 
with  hydrogen  sulphide.  The  filtrate  from  the  barium-lead 
sulphates  was  also  treated  with  hydrogen  sulphide,  and  the 
resulting  precipitate  containing  lead,  bismuth,  Ra  F,  etc., 
added  to  the  former.  The  combined  precipitate  was  con- 
verted into  nitrates,  then  into  carbonates,  and  then  into 
nitrates  again.  The  nitrates  were  precipitated  by  sodium 
hydroxide,  enough  of  the  reagent  added  to  redissolve  the  lead, 
and  the  solution  filtered.  The  lead,  all  of  which  was  in  the 
nitrate,  was  converted  into  a  carbonate,  then  into  a  nitrate, 
and  the  solution  evaporated  to  dryness.  At  this  time  it 
possessed  no  appreciable  activity,  and  was  set  aside  until 
Ra  E2  should  have  grown  to  maximum  amount. 

Before  measuring  the  activity  of  Ra  E2  it  was  necessary 
to  separate  it  from  the  very  considerable  amount  of  solid 
matter,  over  125  mg,  associated  with  it,  as  the  absorption  of 
the  soft  rays  of  radium  E2  takes  place  readily.  The  separa- 
tion was  made  in  the  following  manner. 

When  to  a  lead  nitrate  solution  containing  radium  D, 
Et,  E2,  and  F,  sodium  hydroxide  is  added,  complete  pre- 
cipitation takes  place,  but  upon  addition  of  excess  of  the  re- 
agent only  the  lead  and  Ra  D  redissolve,  provided  there  is 
sufficient  solid  matter  in  the  residue  to  afford  a  nucleus.  The 
separation  becomes  quantitative  when  a  drop  of  ferric  chloride 
solution  is  added.  The  solid  residue  was  filtered  off,  dried, 
and  measured  at  once,  so  that  no  correction  needed  to  be 
made  for  decay. 


526  Stewart  J.  Lloyd 


Weight  of  uraninite 

Activity 

Act.  perg.  mineral 

Act.  per  g.  Uran. 

IO 

35-4 

I 
3-54 

6.1 

Percentage  of  total  /?  activity  of  uraninite  due  to  Ra  E2,  10.9. 

The  ft  activity  of  uraninite  per  gram  uranium  was  found 
to  be  55.75  in  arbitrary  units.  The  activities  of  the  several 
constituents  in  the  same  units,  and  in  percentages  are 

Uranium  X  17.9  32-i% 

Radium  B  9.0  16.  i 

Radium  C  20.1  36 .  i 

Radium  E2  6.1  10.9 

53-i  95-2% 

Whether  the  missing  4.8  percent  is  contributed  by  some 
constituent  as  yet  unknown,  or  is  due  to  experimental  errors, 
is  hard  to  say. 

It  was  expected  that  the  total  activities  as  given  above 
would  show  some  intimate  relation  to  the  absorbability  of  the 
various  rays.  Such  is  hardly  the  case  however,  as  the  follow- 
ing table1  shows.  The  first  column  contains  the  thicknesses, 
in  cm  of  aluminium  foil,  required  to  reduce  the  activity  to 
half  value  in  each  case,  the  second  column  the  total  activities. 

Uran  X  0.048  32.1 

6.014 
RaB  0.053  J5-9 

o . 0078 
RaC  0.0534  35-9 

0.0131 
Ra  E2  0.016  10.9 

Indeed  the  rays  from  any  one  substance  do  not  appear  to 
be  homogeneous,  so  that  to  obtain  comparable  numbers  for 
their  absorbabilities  it  would  be  necessary  to  know  much  more 
accurately  than  we  do  at  present  the  relative  amounts  of  the 
hard  and  soft  rays  in  each. 

It  should  be  noted  that  account  is  taken  only  of  those 
rays  which  produce  appreciable  ionization  after  passing 
through  0.044  mm  of  aluminium  foil.  It  is  quite  possible, 
indeed  probable,  that  other  rays,  like  the  soft  rays  of  U  X, 

1  Le  Radium  6,  i  (1909). 


The  Beta  Activity  of  Uraninite  527 

exist,  and  in  establishing  the  numbers  of  /?  particles 
given  off  by  each  substance  such  rays  would  have  to  be  taken 
into  account.  Hahn1  has  recently  advanced  the  hypothesis 
that  a  single  radioactive  substance  is  capable  of  emitting  rays 
of  one  kind  only,  either  homogeneous  a  or  homogeneous  /? 
rays.  If  such  is  the  case,  the  number  of  accepted  radioactive 
substances  will,  obviously,  have  to  be  greatly  increased, 
especially  the  number  of  those  emitting  ft  particles. 

Although,  as  was  stated  at  the  beginning  of  this  article, 
the  absolute  ionization  current  due  to  the  /?  activities  of  the 
constituents  of  uraninite  could  not  be  determined  with  ex- 
actness, it  is  possible,  however,  from  the  measurements 
made,  to  assign  a  lower  limit  to  it  in  each  case.  According 
to  McCoy  and  Ross2  the  total  activity  of  i  gram  of  uranium 
is  equal  to  that  of  796  square  cm  of  a  thick  film  of  U3O8.  In 
the  electroscope  used  throughout  the  present  work,  the  U  X 
associated  with  i  gram  uranium  in  radioactive  equilibrium 
was  found  to  possess  an  activity  equal  to  that  of  7.53  sq.  cm 
(a  only)  of  a  thick  film  of  U3O8.  Hence,  the  hard  rays  of  U  X 
in  radioactive  equilibrium  with  i  gram  uranium  have  an 
activity  equal  to  that  of  0.00946  gram  uranium,  and  hence  an 
ionization  current  of  4.36  io~12  amp.  Since  U  X  furnishes 
32.1  per  cent  of  the  total  ionization  due  to  the  /?  activity  of 
uraninite,  the  /?  activity  of  the  latter  is  equal  to  the  a  activity 
of  0.0295  gram  of  uranium,  and  gives  an  ionization  current 
of  1.358  io~"  amp.  If  the  soft  rays  of  U  X  be  included,  the 
figures  for  U  X  become  0.0129  and  5.95  X  io~12;  for  uraninite 
0.0329  and  1.516  X  io~~u.  If  U  X  is  genetically  connected 
with  radium,  and  if  the  periods  of  the  two  be  taken  as  22  days, 
and  1760  years  respectively,  the  weight  of  U  X  in  equilibrium 
with  i  gram  uranium  is  1.116  X  io~6  gram.  Weight  for 
weight  therefore  U  X  (hard  rays)  is  at  least  8.48  X  io7  as 
active  as  uranium.  Including  the  soft  rays  it  is  11.02  X  io7 
as  active  as  uranium. 

Kent  Chem.  Lab., 
Uni-v.  of  Chicago 


1  Phys.  Zeit.,  9,  697. 

2  Jour.  Am.  Chem.  Soc.,  29,  1698  (1907) 


THE  ESTIMATION  OF  RADIUM 


BY   STEWART  J.    LLOYD 

In  the  course  of  an  investigation  which  involved  frequent 
determinations,  by  the  emanation  method,  of  the  amount  of 
radium  present  in  minerals  and  in  solutions,  some  irregulari- 
ties were  noticed,  which  led  to  the  examination  of  the  con- 
ditions necessary  for  the  accurate  determination  of  radium 
in  this  way.  The  facility  with  which  radium  may  be  esti- 
mated by  means  of  its  emanation,  wTherein  it  is  unique  among 
radioactive  substances,  renders  the  method  of  considerable 
importance.  Indeed  so  simple  and  convenient  is  the  process 
that  it  bids  fair  to  be  used  as  an  indirect  means  of  determining 
substances  other  than  radium,  just  as  the  iodine -thiosulphate 
titration  is  employed  in  the  estimation  of  substances  ranging 
from  copper  to  chlorine.  At  present  it  undoubtedly  furnishes 
the  simplest  method  of  determining  uranium  in  minerals. 
Unlike  most  other  methods  of  analysis,  too,  it  has  the  ad- 
vantage that  the  sample  is  not  destroyed  in  the  course  of  the 
work,  but  may  be  re-examined  any  number  of  times.  It 
is  quite  within  the  range  of  possibility,  therefore,  that  the 
gas-electroscope  will  take  its  place  in  the  analytical  laboratory 
along  with  the  polariscope  and  the  refractometer. 

The  method  in  question  is  well  known,  in  outline  at  least, 
to  all  those  concerned  with  measurements  in  radioactivity. 
The  solution  containing  radium  is  boiled  to  expel  all  emanation 
present,  sealed  up  for  a  definite  time,  usually  several  days, 
to  permit  the  emanation  to  accumulate,  and  the  emanation 
then  drawn  off  into  a  gas-electroscope  where  its  activity  is 
measured.  Since  in  a  radium  solution  which  has  been  freed 
from  emanation  the  latter  grows  to  half  value  in  3.75  days, 
it  is  possible  to  calculate  the  total  maximum  value  of  the 
activity  from  the  formula 

i==i0(i—«-*0 

where   "I"   is   the   activity  observed    (the  reciprocal  of  the 
time  of  discharge),    "I0"    the    maximum    activity,    "A"    the 


The  Estimation  of  Radium 


477 


decay  constant,  and  "/"  the  time;  and  by  standardizing  the 
electroscope  from  time  to  time  with  a  solution  of  known 
radium  content,  it  is  possible  to  determine  the  actual  amount 
of  radium  present  in  any  case. 

Rutherford  appears  to  have  been  the  first  to  use  this 
method.  After  him,  Boltwood,  McCoy,  Joly,  and  numerous 
others  have  practiced  it  with  various  modifications.  The 
present  article  is  not  concerned  with  the  mode  of  transferring 
the  emanation  from  the  vessel  containing  it  to  the  electro- 
scope, which  has  been  the  point  of  difference  between  them, 
but  with  the  effect  which  the  state  of  the  solution  exercises 
upon  the  giving  up  of  the  emanation. 

It  had  been  noticed  that  the  presence  of  foreign  sub- 
stances exerted  a  marked  effect  on  the  accuracy  of  the  esti- 
mation. To  test  the  extent  of  this  effect  and  to  determine  the 
conditions  under  which  accurate  results  might  be  obtained, 
the  following  experiments  were  made. 

A  dilute  radium  solution  prepared  from  uraninite  residues, 
and  therefore  containing  barium,  was  made  up,  and  10  cc 
of  it  placed  in  each  of  several  150  cc  flasks,  100  cc  of  water 
added,  the  solution  boiled  vigorously  for  fifteen  minutes, 
and  then  small  quantities  of  the  following  reagents  added, 
one  to  each  flask.  The  flasks  were  then  tightly  stoppered, 
and  allowed  to  stand  for  several  days.  The  emanation  pro- 
duced in  that  time  was  then  measured  and  the  maximum 
amount  calculated.  The  results  are  found  in  the  following 
table. 


No. 

Reagent 

Time  of  discharge  for  maximum 
Sec. 

I 

H2S04 

35-6 

2 

HC1 

18.4 

3 

HNO3 

18.2 

4 

Na2CO3 

27.7 

5 

K2CrA 

19.0 

6 

KOH 

19.6 

7 

MoO3 

18.7 

8 

HP 

19.6 

9 

Hg 

23-3 

478  Stewart  J.  Lloyd 

From  this  table  it  is  evident  that  only  in  the  presence 
of  hydrochloric  or  of  nitric  acid  is  the  emanation  completely 
evolved.  Sulphuric  acid  and  sodium  carbonate,  which  pre- 
cipitate the  sulphates  and  carbonates  of  barium  and  radium, 
hinder  very  noticeably  the  evolution  of  emanation.  The 
other  reagents  have  but  slight  effect,  mercury  more  than  the 
rest. 

To  determine  whether  other  reagents  which  effected 
precipitation  in  the  solution  had  the  same  effect  as  sulphuric 
acid  and  sodium  carbonate,  some  of  the  solutions  which  had 
been  previously  used,  after  boiling  to  remove  emanation, 
were  treated,  respectively  with  the  following  reagents,  sealed 
up  for  some  days  and  the  emanation  measured  as  before. 

Discharge 


To  No.    i  was  added  BaCl2  producing  BaSO4  27.35 

AgNO3        "          AgCl  18.2 

CaCO3  CaCO3  24 . 9 

BaCl2  BaCO3  50.2 

Pb(NO3)2    "  PbCr64  19.1 

AgN03        «      .     Ag,0  18.5 

It  will  be  seen  from  the  table  that  the  production  of  a 
precipitate  in  a  solution  does  not  necessarily  mean  an  impair- 
ment of  the  accuracy  of  the  determination.  Only  in  the  case 
of  sulphates  and  carbonates  is  the  interference  with  the  evolu- 
tion marked.  Further  experiments  were  therefore  made 
to  determine  if  possible  the  cause  of  this  difference. 

Four  similar  radium  solutions  were  made  up,  sealed  in 
the  usual  way,  and  the  emanation  measured  after  an  interval. 


Discharge 
Sec. 


No.  i  contained  no  H2SO4 
"2         "        5  cc   H2SO4  (dilute) 

3         "          "         "  "     plus  BaCl2 


4  Na2CO: 


54 

63 

149 

74 


The    radium    solutions    of    course    contained    originally 
a  small  amount  of  BaCl2.     It  is  apparent  from  the  table  that 


The  Estimation  of  Radium 


479 


the  greater  the  amount  of  BaSO4,  formed  the  less  emanation 
is  given  off. 

These  experiments  did  not  however  throw  any  light  upon 
the  mechanism  of  the  retention  of  emanation,  so  another 
series  was  made.  To  each  of  four  radium-barium  chloride 
solutions  were  added  equal  amounts  of  BaCl2,  and  then  equal 
amounts  of  H2SO4  (excess)  were  run  in,  with  stirring,  from 
a  burette,  under  identical  conditions  except  that  No.  2  was 
precipitated  cold,  the  others  hot. 

1.  The    pptd.     BaSO4    was    filtered    immediately,    and 
both  the  precipitate  and  the  filtrate  sealed  up  at  once. 

2.  As  No.  i  except  that  precipitation  was  made  in  cold. 

3.  Stirred  continuously  for  thirty  hours,  after  precipita- 
tion, then  treated  as  i. 

4.  Heated  continuously  for  thirty  hours  after  precipita- 
tion, then  treated  as  i. 

After  a  suitable  interval  the  radium  contents  of  filtrates 
and  precipitates  were  determined. 


No. 

Residue 
Sec. 

Filtrate 
Sec. 

I 

500 

I2OOO 

2 

420 

11400 

3 

144.2 

10800 

4 

133-6 

I  1  100 

This  table  indicates  that  in  every  case  practically  the 
same  amount  of  radium  remains  unprecipitated  by  the  sul- 
phate, but  that  the  readiness  with  which  the  emanation  is 
given  off  from  the  part  that  is  precipitated  depends  very 
largely  upon  the  treatment  to  which  it  is  subjected,  stirring 
and  heating,  especially  the  latter,  facilitating  the  evolution 
very  markedly. 

A  similar  set  of  experiments  involving  the  precipitation 
of  BaCO3  instead  of  BaSO4  was  made.  Sodium  carbonate 
in  excess  was  added  to  each  of  three  radium-barium  chloride 
solutions. 

No.  i  was  filtered  at  once. 


Stewart  J.  Lloyd 


No.  2  was  heated  for  fifty  hours  and  then  filtered. 
No.  3  was  stirred  for  fifty  hours  and  then  filtered 
Upon  examination  for  emanation  they  gave: 


No. 

Residue 
Sec. 

Filtrate 
Sec. 

I 

348 

2970 

2 

144 

I2OO 

3 

339 

2724 

The  results  here  are  quite  analogous  to  those  obtained 
Avith  BaSO4  except  that  stirring  does  not  seem  to  be  so  effi- 
cacious, and  the  precipitation  of  radium  by  the  carbonate 
is  not  so  complete. 

A  further  experiment  was  made  to  determine  what 
effect  the  physical  condition  of  BaSO4  has  upon  the  retention 
of  emanation.  A  hydrochloric  acid  solution  of  radium  which 
gave  an  emanation  content  corresponding  to  a  time  of  dis- 
charge of  1 60  seconds  was  precipitated  with  sulphuric  acid 
and  barium  chloride,  and  its  emanation  content  measured 
at  intervals  of  four  days.  The  times  of  discharge  correspond- 
ing to  the  maximum  amounts  were: 


Days 


Sec. 


4 

8 

12 

16 

20 


370 
J75 
165 
157 
163 


BaSO4  previously  made  and  heated  for  some  time  was 
then  added  to  the  solution  and  thoroughly  shaken  with  it. 
The  time  of  discharge  was  not  however  affected,  remaining 
163  seconds. 

To  ascertain  whether  or  not  the  total  amount  of  emana- 
tion was  finally  obtained  from  solutions  in  which  sulphates 
had  been  precipitated,  two  solutions  containing  the  same 
amount  of  radium,  the  first  acid  with  hydrochloric  acid,  the 


The  Estimation  of  Radium 


481 


second  having  a  heavy  precipitate  of  BaSO4  produced  in  it, 
were  measured  from  time  to  time. 


Days 

HC1  solution 
Sec. 

BaSO4  solution 
Sec. 

4 

57 

167 

9 

58 

87 

13 

56-5 

62 

17 

58 

59 

22 

58.5 

58 

Conclusion. 

For  the  accurate  determination  of  radium  by  the  emana- 
tion method  the  presence  of  HC1  or  HNO3  is  necessary. 

If  the  sulphate  or  carbonate  of  barium  is  present  in  the 
solution,  prolonged  boiling  or  repeated  determinations  will 
be  necessary  to  ensure  the  extraction  of  the  total  emanation. 

The  retention  of  emanation  by  the  freshly  precipitated 
BaSO4  is  doubtless  mechanical  only,  and  is  due  to  the  en- 
tanglement of  the  radium  chloride  or  sulphate  within  the 
fine  almost  amorphous  precipitate.  Recrystallization  under 
the  influence  of  heat  releases  the  radium,  and  permits  the 
removal  of  the  emanation. 

Kent  Chem.  Lab., 
Univ.  of  Chicago 


OF 

UNIVERSITY 

Of 


The  preceding  work  was  done  at  the  suggestion  and  under 
the  direction  of  Prof.  H.  N.  McCoy,  whose  encouragement  and 
advice  are  gratefully  acknowledged  by  the  author. 


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